Schedule II Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for doubtful accounts and returns
Changes in Valuation and Qualifying Accounts
Balance at Beginning of Period		$ 77
Charged to Costs and Expenses			$ 106
Deductions		77	29
Balance at End of Period			77
Deferred tax valuation allowance
Changes in Valuation and Qualifying Accounts
Balance at Beginning of Period	$ 7,136	122,966	132,263
Charged to Costs and Expenses	(441)	(115,831)	(7,765)
Deductions	(140)	(1)	1,532
Balance at End of Period	$ 6,835	$ 7,136	$ 122,966